Gear-change mechanisms of this kind have been disclosed in German patent document G 78 02 241 where parts of the gear-shifting means have been designed to perform several functions, so that despite the gear-changing operations of the basic drive which are basically the same for the higher as well as for the lower range, each gear of the gear-change transmission can be associated with a specific position of the hand gear-shift lever.
In general such drives are designed to have two ranges, for instance a 4-gear basic drive has altogether 8 forward gears in the two ranges of which in this case the gears 1 to 4 are in the lower range and the gears 5 to 8 are in the higher range, whereby the shifting of the 4 gears of the basic drive and therefore of one range is effected according to the usual H-type gear-shifting pattern. By employing for instance a second striker engaging in gear selector rods of the basic drive, the shifting of the 4 gears of the higher range can be effected according to an identical H-type gear-shifting pattern as the lower range, but laterally offset and adjacent to it, so that the pattern as a whole resembles a double "H" (HH pattern).
If the gear-change mechanism concerned comprises an independent change-over of the range group drive which is activated when the gear-shift lever changes over from one "H" pattern section to the neighboring one, then the gear-changing operations of such a group drive can be carried out with the same simplicity and logic as with a simple drive, but with 8 forward gears in 4 associated gear-chains. The reverse gear has its own gear chain which is used only in the lower range and which may include a crawler or very slow forward gear.
In order to limit the size of such gear-change mechanisms, but to ensure that the engaged gear can be safely recognized on the gear-shift lever, the space-oriented position is superimposed by power orientation. Due to the varying forces or force-free slot-in zones the operator receives additional clear information of the selected gear-chain so that the distances of the gear-chains can be reduced while simultaneously improving the orientation for the selected gear-chain. The spatial orientation which is still possible, further increases his confidence in having chosen the right gear and in any case allows him to differentiate between the gears within a gear-chain.
Despite the advantage of such a gear-change mechanism in the area of the driver's cabin, considerable space problems arise in the area of the gear-change housing in or on the gearbox and in the gearbox itself. The relatively many elements which such gearboxes require in order to be reliable and safe considering the many different adaptations to various vehicles, need space, which is often no longer available with different optimum vehicle designs.